But over and above the running supply, the Croton lake created by the dam, is estimated to contain 100,000,000 gallons for each foot in depth from the surface, and this may be drawn down five or six feet, yielding as many hundred million gallons. The receiving reservoir will contain 158 millions of gallons, and the distributing reservoir 19 millions altogether forming an aggregate surplus, in case of excessive and long continued drought, sufficient for any possible emergency. The work performed during the last six months of the year is thus summarily stated :

" 1st. The whole length of aqueduct, arched and complete, is 59,169 feet Aqueduct.

or eleven and one fifth miles. That completed on the first of July last was about two miles. The increase, in this part of the work, since our last report, is nine and one fifth miles of aqueduct complete.

2d. Side Wall. The length of side wall, ready to receive the arch, exclusive of that already arched, is 1443 feet.

3d. Culverts. There are 79 completed and in use. Their aggregate culverts

length is 5476 feet. The number completed at our last report was twenty-two, and their length 1825. Increase, 57 culverts. The number now partly finished is ten, and their length in feet 652. The number partly finished at our last report was seven; length 578. Increase, 3 culverts in progress.

Tunnels. The number of tunnels excavated throughout is three. Their aggregate

length 667 feet. There are, besides, seven tunnels partly finished, measuring 1187 feet of excavation; making .an aggregate of tunnelling of 1854 feet. The number complete at our last report was three, arid the length 670 feet, together with five partly finished,